Device structure of carbon fibers and manufacturing method thereof

ABSTRACT

An aggregate structure of carbon fibers, organized by a plurality of carbon fibers, includes, an aggregate of the carbon fibers aligned in a lengthwise direction, in which a density of the carbon fibers at one side end is different from a density of the carbon fibers at the other side end.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of Application PCT/JP2007/054549, filed on Mar.8, 2007, now pending, the contents of which are herein whollyincorporated by reference.

BACKGROUND

The present disclosure relates to a device structure of carbon fibersand a manufacturing method thereof.

Carbon nanotubes (CNT) are excellent in terms of electric conductivity,thermal conductivity and a mechanical characteristic and therefore taketrial applications to a variety of fields. Hence, an expectation is thatthe carbon nanotubes will be applied to an electronic device, a heatradiation device, wiring for an LSI (Large Scale Integration), a channelof a transistor, a heat radiation bump and an electron emission source.It is also expected that especially the carbon nanotubes grown invertical alignment will be applied to the wiring and the heat radiation.Note that a mainstream method of attaining the vertically-aligned growthof the carbon nanotubes is a chemical vapor deposition (CVD) method atthe present, and it is generally practiced that the carbon nanotubes(CNT) are grown directly on a desired substrate. The method of attainingthe vertically-aligned growth of the carbon nanotubes is exemplifiedsuch as a thermal CVD method, a plasma CVD method and a hot filament CVDmethod. Further, a thermal decomposition method of SiC is exemplified asa method of acquiring the carbon nanotubes close to closest packing.

In the application to the carbon nanotubes, the carbon nanotubes grownin vertical alignment on the substrate are utilized in many cases.Applied examples of the carbon nanotubes are, e.g., the wiring for theLSI and the heat radiation bumps. In the case of applying the carbonnanotubes, it is desirable that the carbon nanotubes having the highestpossible density be grown on the substrate in terms of reducing a wiringresistance and improving heat radiation efficiency. The carbon nanotubesgrown in vertical alignment by the conventional technique have, however,a low density. Further, some segments of the neighboring carbonnanotubes abut on each other, however, all of the carbon nanotubes arenot necessarily brought into contact with each other. Namely, a problemis that an interval between the neighboring carbon nanotubes isexpanded. The growth of the carbon nanotubes having the high density isnot generally easy, and a volume occupancy rate of the carbon nanotubesgrown in vertical alignment by the conventional technique is on theorder of 10%. Further, in the thermal decomposition method of SiC, athermal treatment temperature is 1200° C.-2200° C. It is thereforedifficult to select the substrate and make process matching with otherdevices.

SUMMARY

According to an aspect of an embodiment, there is an aggregate structure(a fibril structure) of carbon fibers (carbonaceous fibers), organizedby a plurality of carbon fibers, includes: an aggregate of the carbonfibers aligned in a lengthwise direction, in which a density of thecarbon fibers at one side end is different from a density of the carbonfibers at the other side end. According to the present disclosure, thedensity, at both side ends, of the aggregate of the carbon fibersdiffers at one side end and the other side end.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a case in which carbon nanotubes 1 aregrown in vertical alignment by a conventional technique.

FIG. 2 is a front view of the carbon nanotubes 1 in the case where thecarbon nanotubes 1 are grown in vertical alignment by the conventionaltechnique.

FIG. 3 is atop view of the carbon nanotubes 1 in the case where thecarbon nanotubes 1 are grown in vertical alignment by the conventionaltechnique.

FIG. 4 is a view showing a growth method of the carbon nanotubes 1 in afirst embodiment.

FIG. 5 is a view showing an example in which a carbon nanotube group 5is grown.

FIG. 6 is a view showing how the carbon nanotube group is dipped into acontainer 6 filled with a resin containing an organic solvent.

FIG. 7 is a view showing how the carbon nanotube group 5 is dipped intothe container 6 filled with the resin containing the organic solvent.

FIG. 8 is a view showing how the carbon nanotube group 5 is dipped intothe container 6 filled with the resin containing the organic solvent.

FIG. 9 is a view showing how the carbon nanotube group 5 is dipped intothe container 6 filled with the resin containing the organic solvent.

FIG. 10 is a front view of the carbon nanotube group 5 in which one sideends of the carbon nanotubes 1 are so formed as to lean on each other.

FIG. 11 is a top view of the carbon nanotube group 5 in which one sideends of the carbon nanotubes 1 are so formed as to lean on each other.

FIG. 12 is a front view of the carbon nanotube group 5 in which one sideends of the carbon nanotubes 1 are so formed as to lean on each other.

FIG. 13 is a top view of the carbon nanotube group 5 in which one sideends of the carbon nanotubes 1 are so formed as to lean on each other.

FIG. 14 is a view showing a space where none of the carbon nanotubes 1exist.

FIG. 15 is a view showing a plurality of carbon nanotube groups 5 havingdifferent densities.

FIG. 16 is a front view showing a case in which the plurality of carbonnanotube groups 5 having the different densities is aligned so that thehighly-densified side ends are disposed in alternate directions.

FIG. 17 is a view showing a post-patterning iron film 8.

FIG. 18 is a view showing the carbon nanotube groups 5 that are grown invertical alignment on a silicon substrate 7 with an oxide film.

FIG. 19 is a view showing a process of adhering a solvent to the carbonnanotube groups 5.

FIG. 20 is a view showing the process of adhering the solvent to thecarbon nanotube groups 5.

FIG. 21 is a view showing the process of adhering the solvent to thecarbon nanotube groups 5.

FIG. 22 is a view showing the process of adhering the solvent to thecarbon nanotube groups 5.

FIG. 23 is a view showing the process of adhering the solvent to thecarbon nanotube groups 5.

FIG. 24 is a view showing the process of adhering the solvent to thecarbon nanotube groups 5.

FIG. 25 is a front view of the carbon nanotube groups 5 in which oneside ends of the carbon nanotubes 1 are so formed as to lean on eachother.

FIG. 26 is a view showing the highly-densified carbon nanotube groups 5and a substrate 20.

FIG. 27 is a view showing the substrate 20 and a structure of asubstrate 23.

FIG. 28 is a view showing a structure in which a substrate 23 with alow-melting metal film and the substrate 20 are superposed on eachother.

FIG. 29 is a view showing a structure in which the carbon nanotubegroups 5 is peeled off the substrate 20, and the substrate 23 with thelow-melting metal film is tightly fitted to the carbon nanotube groups5.

FIG. 30 is a view showing a step in a case where a densification processshown in a third embodiment is executed on the carbon nanotube groups 5.

FIG. 31 is a view showing the step in the case where the densificationprocess shown in the third embodiment is executed on the carbon nanotubegroups 5.

FIG. 32 is a view showing the step in the case where the densificationprocess shown in the third embodiment is executed on the carbon nanotubegroups 5.

FIG. 33 is a view showing the step in the case where the densificationprocess shown in the third embodiment is executed on the carbon nanotubegroups 5.

FIG. 34 is a structural view illustrating conventional transistorpackaging.

FIG. 35 is a structural view showing flip-chip packaging.

FIG. 36 is a structural view showing the flip-chip packaging.

FIG. 37 is a view showing a structure of an aluminum nitride substrate50 formed with electrodes 51.

FIG. 38 is a view showing the structure of the aluminum nitridesubstrate 50 formed with the carbon nanotube groups 5.

FIG. 39 is a view showing the structure of the aluminum nitridesubstrate 50 formed with the highly-densified carbon nanotube groups 5.

FIG. 40 is a view showing the structure of the aluminum nitridesubstrate 50 formed with the carbon nanotube groups 5 in which lengthsof the carbon nanotubes 1 are not uniform.

FIG. 41 is a view showing the structure of the aluminum nitridesubstrate 50 on which an interlayer insulating film 60 is deposited soas to cover the carbon nanotube groups 5.

FIG. 42 is a view showing the structure of the aluminum nitridesubstrate 50 after polishing the carbon nanotube groups 5 and interlayerinsulating film 60.

FIG. 43 is a view showing the structure of the aluminum nitridesubstrate 50 provided with a high-power transistor chip 40.

FIG. 44 is a view showing a structure of an LSI (Large Scale IntegratedCircuit) 70.

FIG. 45 is a view showing a structure of a substrate 74 and an LSIsubstrate 75 on which the carbon nanotube groups 5 are grown.

FIG. 46 is a view showing a structure in which the substrate 74 and theLSI substrate 75 are superposed on each other.

FIG. 47 is a view showing a structure in which a gap between thesubstrate 74 and the LSI substrate 75 is filled with an interlayerinsulating film 80.

FIG. 48 is a view showing a structure of the substrate 74 on which theinterlayer insulating film 80 is deposited so as to cover the carbonnanotube groups 5.

FIG. 49 is a view showing a structure in which distal ends of the carbonnanotube groups 5 are protruded.

FIG. 50 is a view showing the structure of the LSI substrate 75, inwhich the carbon nanotube groups 5 and the interlayer insulating film 80are polished.

FIG. 51 is a view showing the structure of the LSI substrate 75 formedwith copper wiring 71.

FIG. 52 is a view showing the structure of the LSI substrate 75 formedwith copper wiring 71 and a structure of the substrate 74.

FIG. 53 is a view showing a structure in which the substrate 74 and theLSI substrate 75 formed with the copper wiring 71 are superposed on eachother.

FIG. 54 is a view showing a structure in which the carbon nanotubegroups 5 are tightly fitted to the copper wiring 71 formed on the LSIsubstrate 75.

FIG. 55 is a view showing the structure of the LSI substrate 75, inwhich the carbon nanotube groups 5 and the interlayer insulating film 80are polished.

DETAILED DESCRIPTION

A best mode (which will hereinafter be termed an embodiment) forcarrying out the present disclosure will hereinafter be described withreference to the drawings. Configurations in the following embodimentsare exemplifications, and the present disclosure is not limited to theconfigurations in the embodiments.

FIG. 1 is a diagram illustrating a case of a vertically-aligned growthof carbon nanotubes 1 by the conventional technique. As illustrated inFIG. 1, a large quantity of carbon nanotubes 1 are grown. Someneighboring carbon nanotubes 1 are not, however, brought into contactwith each other. FIG. 2 is a front view of the carbon nanotubes 1 in thecase of the vertically-aligned growth of the carbon nanotubes 1 by theconventional technique. FIG. 3 is a top view of the carbon nanotubes 1in the case of the vertically-aligned growth of the carbon nanotubes 1by the conventional technique. As shown in FIGS. 2 and 3, there areintervals between the neighboring carbon nanotubes 1. Namely, gaps occurbetween the neighboring carbon nanotubes 1. All the carbon nanotubes 1are not, however, necessarily isolated without abutting on each other.The vertically-aligned growth entails the contact portions as the casemay be. Especially if the carbon nanotubes are thinned, thevertically-aligned growth is hard to be attained unless some contactportions are produced. Even in this case, the gaps occur between theadjacent carbon nanotubes 1.

First Embodiment

A growth technique of the carbon nanotubes 1 according to a firstembodiment will be illustrated with reference to FIGS. 4 through 11. Asshown in FIG. 4, a titanium (Ti) layer 3 is formed on a siliconsubstrate 2. Then, a cobalt (Co) layer 4 is formed on the titanium layer3. In this case, the cobalt layer 4 undergoes patterning on the order of1 μm in diameter. In the first embodiment, the cobalt layer 4 undergoesthe patterning on the order of 1 μm in diameter and may also, withoutbeing limited to this size, be subjected to the patterning to an anysize. The patterning of the cobalt layer 4 enables the control ofpositions where the carbon nanotubes 1 are grown.

Next, the silicon substrate 2 formed with the titanium layer 3 and thecobalt layer 4 is introduced into a thermal CVD chamber. Then, a mixturegas (9:1) of argon (Ar) and acetylene (C2H2) is introduced under 1 kPainto the thermal CVD chamber.

Moreover, after stabilizing a pressure within the thermal CVD chamber,the silicon substrate 2 is heated at 510° C. for 30 min. Next, thesilicon substrate 2 is kept in a state of being heated at 510° C.Through the process described above, the carbon nanotubes 1 are grown onthe cobalt layer 4. FIG. 5 is a view showing a carbon nanotube group 5grown on the cobalt layer 4. The carbon nanotube group 5 represents anaggregation of the carbon nanotubes 1 grown on the cobalt layer 4.

As illustrated in FIG. 5, the carbon nanotubes 1 on the cobalt layer 4are grown in the vertical direction. FIG. 5 shows an example of how thecarbon nanotube group 5 is grown, however, the number of the carbonnanotubes 1 is not limited to this illustrated number. Further, in thefirst embodiment, the growth of the carbon nanotubes 1 involves usingcobalt as a catalyst metal. The catalyst metal is not, however, limitedto cobalt, and may involve employing transition metals such as iron (Fe)and nickel (Ni). Moreover, the growth method of the carbon nanotubes 1may involve using a chemical vapor deposition (CVD) method, a hotfilament CVD method and a plasma CVD method.

Next, the carbon nanotube group 5 is dipped in a resin containing anorganic solvent (which is a solvent containing an adhesive substancedifferent from the carbon nanotube). To be specific, the carbon nanotubegroup 5 shown in FIG. 5 is dipped into a container 6 filled with theresin containing the organic solvent. In the case of dipping the carbonnanotube group 5 in the resin containing the organic solvent, the carbonnanotube group 5 is dipped together with the silicon substrate 2. FIG. 6is a view showing that the carbon nanotube group 5 is dipped in theresin containing the organic solvent.

For example, as illustrated in FIG. 6, the carbon nanotube group 5 isdipped up to A-segments into the container 6 filled with the resincontaining the organic solvent. Further, for instance, as shown in FIG.7, the carbon nanotube group 5 is dipped up to B-segments into thecontainer 6 filled with the resin containing the organic solvent. FIGS.6 and 7 are views each showing a state immediately after the carbonnanotube group 5 has been dipped into the container 6 filled with theresin containing the organic solvent.

In FIG. 6, the dipped segment of the carbon nanotube 1 is set toapproximately half a length of the carbon nanotube 1. The dipped segmentconnotes a dipped portion of the carbon nanotube 1 when dipped into thecontainer 6 filled with the resin containing the organic solvent. InFIG. 7, the dipped segment extends to approximately 20% of the length ofthe carbon nanotube 1. The dipped segment can be properly variedcorresponding to a type of the organic solvent and a type of the resin.

In FIGS. 6 and 7, the proximal portions (one side ends abutting on thesilicon substrate 2) of the carbon nanotube group 5 corresponds to thedipped segments. Further, in the case of dipping the carbon nanotubegroup 5 into the container 6 filled with the resin containing theorganic solvent, the distal portions (the other side ends which do notabut on the silicon substrate 2) can be also dipped.

For example, as illustrated in FIG. 8, the distal portion of each carbonnanotube 1 is used as the dipped segment. In this case, as illustratedin FIG. 8, the carbon nanotube group 5 is dipped up to C-segments intothe container 6 filled with the resin containing the organic solvent.Moreover, for instance, as illustrated in FIG. 9, the carbon nanotubegroup 5 is dipped up to D-segments into the container 6 filled with theresin containing the organic solvent. FIGS. 8 and 9 are views eachshowing a state immediately after the carbon nanotube group 5 has beendipped into the container 6 filled with the resin containing the organicsolvent. In FIG. 8, the dipped segment of the carbon nanotube 1 is setto approximately half a length of the carbon nanotube 1. In FIG. 9, thedipped segment extends to approximately 20% of the length of the carbonnanotube 1.

A period of time, for which the carbon nanotube group 5 is dipped in theresin containing the organic solvent, is set to approximately 1 min. Inthe first embodiment, the time, for which the carbon nanotube group 5 isdipped in the resin containing the organic solvent, is set toapproximately 1 min, however, the dipping time is not limited to thislength of time. Accordingly, the dipping time may be properly changeddepending on a structure and the number of the carbon nanotubes 1.

For instance, alcohol such as methanol and ethanol is used as theorganic solvent. Further, for example, a thermosetting resin and aphotohardening resin are employed as the resin. The more specific resininvolves, e.g., an epoxy resin.

As shown in FIGS. 6 and 7, in the case of dipping the carbon nanotubegroup 5 into the container 6 filled with the resin containing theorganic solvent, the resin containing the organic solvent fills the gapsbetween the neighboring carbon nanotubes 1. Then, in the carbon nanotubegroup 5 on the silicon substrate 2, one side ends of the respectivecarbon nanotubes 1 are formed as if leaning on each other.

In the case of dipping the carbon nanotube group 5 into the container 6filled with the resin containing the organic solvent, the resincontaining the organic solvent moves by a capillarity to the undippedsegments of the carbon nanotubes 1. Then, the resin containing theorganic solvent moves up to the side ends of the carbon nanotubes 1.When the resin containing the organic solvent moves up to the side endsof the carbon nanotubes 1, the carbon nanotubes 1 comes to a state ofbeing covered with the resin containing the organic solvent.

When the resin containing the organic solvent moves up to the side endsof the carbon nanotubes 1, the neighboring carbon nanotubes 1 lean oneach other by dint of a surface tension. Moreover, in the case ofvolatilizing the organic solvent, the carbon nanotubes 1 come to thestate of being covered with the resin. Then, the respective carbonnanotubes 1 covered with the resin lean on each other by dint of volumeshrinkage when the organic solvent is volatilized. Namely, when theorganic solvent is volatized from the resin containing the organicsolvent, only the resin covers the respective carbon nanotubes 1.Consequently, the individual carbon nanotubes 1 covered with the resinfurther lean on each other.

Accordingly, the respective carbon nanotubes 1 covered with the resinlean on each other, thereby organizing the carbon nanotube group 5.Moreover, when the carbon nanotube 1 abuts on the neighboring carbonnanotube 1, these carbon nanotubes 1 are kept in the state of leaning oneach other. Namely, the carbon nanotubes 1 are kept in the state ofleaning on each other by dint of the resin covering the respectivecarbon nanotubes 1. In other words, the neighboring carbon nanotubes 1are kept in a state of being fixed to each other by the resin coveringthe respective carbon nanotubes 1.

FIG. 10 is a front view of the carbon nanotube group 5, in which theside ends of the individual carbon nanotubes 1 are so formed as to leanon each other. FIG. 10 is the view showing a state after the carbonnanotube group 5 has been dipped into the container 6 filled with theresin containing the organic solvent and pulled up from the container 6.

FIG. 11 is a top view of the carbon nanotube group 5, in which the sideends of the individual carbon nanotubes 1 are so formed as to lean oneach other. FIG. 11 is the view showing a state after the carbonnanotube group 5 has been dipped into the container 6 filled with theresin containing the organic solvent and pulled up from the container 6.

As shown in FIGS. 10 and 11, in the case of dipping the carbon nanotubegroup 5 into the container 6 filled with the resin containing theorganic solvent, one side ends of the respective carbon nanotubes 1 areformed as to lean on each other.

In place of dipping the carbon nanotube group 5 into the resincontaining the organic solvent, the resin containing the organic solventmay be dropped into the carbon nanotube group 5. Further, the resincontaining the organic solvent may be dropped into the carbon nanotubegroup 5 by use of a spin coat method.

In the case of dropping the resin containing the organic solvent intothe carbon nanotube group 5, the resin is dropped so that the respectivecarbon nanotubes 1 are covered with the resin containing the organicsolvent. To be specific, the resin containing the organic solvent isdropped into the segments of the carbon nanotubes 1. In the case ofdropping the resin containing the organic solvent into the segments ofthe carbon nanotubes 1, the resin containing the organic solvent movesby the capillarity to the segments into which the resin containing theorganic solvent is not dropped. When the resin containing the organicsolvent moves to the segments into which the resin containing theorganic solvent is not dropped, the carbon nanotubes come to a state ofbeing covered with the resin containing the organic solvent.

When the resin containing the organic solvent moves to the segments intowhich the resin containing the organic solvent is not dropped, theneighboring carbon nanotubes 1 lean on each other by dint of the surfacetension. Further, in the case of volatizing the organic solvent, thecarbon nanotubes 1 become the state of being covered with the resin.Then, the respective carbon nanotubes 1 covered with the resin lean oneach other by dint of the volume shrinkage when the organic solvent isvolatilized. Namely, when the organic solvent is volatized from theresin containing the organic solvent, only the resin covers therespective carbon nanotubes 1. Consequently, the individual carbonnanotubes 1 covered with the resin further lean on each other.

Accordingly, the respective carbon nanotubes 1 covered with the resinlean on each other, thereby organizing the carbon nanotube group 5.Moreover, when the carbon nanotube 1 abuts on the neighboring carbonnanotube 1, these carbon nanotubes 1 are kept in the state of leaning oneach other. Namely, the carbon nanotubes 1 are kept in the state ofleaning on each other by dint of the resin covering the respectivecarbon nanotubes 1. In other words, the neighboring carbon nanotubes 1are kept in a state of being fixed to each other by the resin coveringthe respective carbon nanotubes 1.

Thus, one side ends of the respective carbon nanotubes 1 covered withthe resin are so formed as to lean on each other. As a result, a densityof the carbon nanotubes 1 of the carbon nanotube group 5 is different onthe distal end side and the proximal end side of the carbon nanotubegroup 5. Namely, the carbon nanotube group 5, in which the density ofthe carbon nanotubes 1 differs at one side end and the other side end,is formed. The density of the carbon nanotubes 1 on the distal end sideof the carbon nanotube group 5 is higher than the density of the carbonnanotubes 1 on the proximal end side of the carbon nanotube group 5.

For example, in the case of using ethanol as the organic solvent and theepoxy resin as the resin, the resin containing the organic solvent isthe epoxy resin diluted with ethanol. Further, a ratio of ethanol andthe epoxy resin is set arbitrarily. A scheme is, however, such that allof the gaps between the neighboring carbon nanotubes 1 are not filledwith the epoxy resin. If all of the gaps between the neighboring carbonnanotubes 1 are filled with the epoxy resin, the neighboring carbonnanotubes 1 do not lean on each other. As a result, in the respectivecarbon nanotubes 1 covered with the resin, one side ends thereof do notbe so formed as to lean on each other. Consequently, a volume of theresin containing the organic solvent is set smaller than a volume of thecarbon nanotube group 5. With this contrivance, it does not happen thatall of the gaps between the neighboring carbon nanotubes 1 are filledwith the epoxy resin.

The first embodiment has exemplified the combination of the organicsolvent and the resin, however, the resin may be replaced with amicrocrystalline material such as nanoporous silica (dielectricmaterial). With this scheme, it is feasible to organize the carbonnanotubes taking the form of leaning on each other with not only theresin but also the dielectric material.

Second Embodiment

A second embodiment of the present disclosure will hereinafter bedescribed with reference to the drawing in FIGS. 12 and 13. The firstembodiment has exemplified the method of organizing the carbon nanotubegroup 5, in which the density of the carbon nanotubes 1 differs at oneside end and the other side end by covering the individual carbonnanotubes 1 with the resin containing the organic solvent. The secondembodiment will exemplify a method of organizing the carbon nanotubegroup 5, in which the density of the carbon nanotubes 1 differs at oneside end and the other side end by covering the individual carbonnanotubes 1 with a metal. Other configurations and operations are thesame as those in the first embodiment. Such being the case, the samecomponents are marked with the same numerals and symbols as those in thefirst embodiment, and their explanations are omitted. Further, thediscussion will refer to the drawings in FIGS. 5 through 11 as thenecessity may arise.

To begin with, the carbon nanotube group 5 is grown on the siliconsubstrate 2 formed with the titanium layer 3 and the cobalt layer 4shown in FIG. 5. The growth method of the carbon nanotube group 5 is thesame as in the first embodiment, and its description thereof is omittedherein. Next, a metal is deposited on each of the carbon nanotubes 1.For instance, the metal deposited on each of the carbon nanotubes 1involves using gold (Au). Further, the metal deposited on each of thecarbon nanotubes 1 may also involve using, e.g., copper (Cu), aluminum(Al), lead (Pb), solder, etc.

In the case of deposing gold on each of the carbon nanotubes 1, gold isdeposited up to a thickness of about 1 nanometer (nm) on the surface ofeach of the carbon nanotubes 1 by a sputtering method. The use of thesputtering method enables gold to be deposited precisely on each of thecarbon nanotubes 1. For example, in the case of employing a sputteringapparatus, a layer thickness of gold to be deposited is set to 1nanometer (nm), thereby depositing gold to the layer thickness of 1nanometer (nm) over each of the carbon nanotubes 1. In this case, thegold-deposited segments of the carbon nanotubes 1 may be setarbitrarily. Moreover, a volume of gold to be deposited is determinedbased on the volume of the deposition-target carbon nanotube group 5.Moreover, in place of depositing the metal on the respective carbonnanotubes 1, the carbon nanotubes 1 may also be dipped into the meltedmetal.

Next, the carbon nanotube group 5 is subjected to a thermal treatment atapproximately 300° C. A melting point of gold is normally over 1000° C.If gold is reduced down to a nano-size, however, the melting point ofgold is lowered. Accordingly, if the carbon nanotube group 5 issubjected to the thermal treatment at approximately 300° C., golddeposited on the carbon nanotubes 1 is melted. Then, the carbonnanotubes 1 are covered with the melted gold. A temperature of thethermal treatment may be obtained empirically or in simulation in thecase of using copper (Cu), aluminum (Al), lead (Pb) and solder as themetal to be deposited on the carbon nanotubes 1.

When gold deposited on the carbon nanotubes 1 gets melted, theneighboring carbon nanotubes 1 covered with gold lean on each other bythe surface tension. Then, the carbon nanotubes 1 covered with gold areso formed as to lean on each other. Accordingly, the carbon nanotubes 1covered with gold lean on each other, thereby organizing the carbonnanotube group 5. Further, when the carbon nanotube 1 abuts on theneighboring carbon nanotube 1, these carbon nanotubes 1 are kept in thestate of leaning on each other. Namely, the carbon nanotubes 1 are keptin the state of leaning on each other by dint of gold covering therespective carbon nanotubes 1. In other words, the neighboring carbonnanotubes 1 are kept in a state of being fixed to each other by goldcovering the respective carbon nanotubes 1.

Thus, one side ends of the respective carbon nanotubes 1 covered withgold are so formed as to lean on each other. As a result, a density ofthe carbon nanotubes 1 of the carbon nanotube group 5 is different onthe distal end side and the proximal end side of the carbon nanotubegroup 5. Namely, the carbon nanotube group 5, in which the density ofthe carbon nanotubes 1 differs at one side end and the other side end,is organized. The density of the carbon nanotubes 1 on the distal endside of the carbon nanotube group 5 is higher than the density of thecarbon nanotubes 1 on the proximal end side of the carbon nanotube group5.

FIG. 12 is a front view of the carbon nanotube group 5, in which theside ends of the individual carbon nanotubes 1 are so formed as to leanon each other. FIG. 13 is a top view of the carbon nanotube group 5, inwhich the side ends of the individual carbon nanotubes 1 are so formedas to lean on each other. As shown in FIGS. 12 and 13, the carbonnanotubes 1 are covered with gold, thereby organizing the carbonnanotube group 5, in which the density of the carbon nanotubes 1 differsat one side end and the other side end. Thus, the process of increasingthe density of the carbon nanotubes 1 of the carbon nanotube group 5 istermed a densification process.

Moreover, the method according to the second embodiment may also beexecuted together with the method according to the first embodiment. Tobe specific, the carbon nanotubes 1 are covered with the metal, whilethe carbon nanotubes 1 are covered with the resin containing the organicsolvent. If more of the metal is deposited on the distal end side of thecarbon nanotubes 1, the carbon nanotube group 5 is dipped into the resincontaining the organic solvent. This process enables acceleration forforming the carbon nanotubes 1 so that one side end thereof lean on eachother. The carbon nanotube group 5, in which the density of the carbonnanotubes 1 differs at one side end and the other side end, can beutilized for, e.g., an electron source of field emission etc.

Third Embodiment

A third embodiment of the present disclosure will be described withreference to the drawing in FIG. 14. The first embodiment and the secondembodiment have exemplified the method of organizing the carbon nanotubegroup 5, in which the density of the carbon nanotubes 1 differs at oneside end and the other side end. The carbon nanotube group 5 having thedifferent densities of the carbon nanotubes 1 is organized by formingone side ends so as to lean on each other. The carbon nanotube group 5having the different densities of the carbon nanotubes 1 connotes thecarbon nanotube group 5 in which the density of the carbon nanotubes 1differs as one side end and the other side end.

The carbon nanotube group 5 having the different densities of the carbonnanotubes 1 includes spaces where none of the carbon nanotubes 1 exist.Namely, as illustrated in FIG. 14, E-areas correspond to the spaceswhere none of the carbon nanotubes 1 exist. In the aggregate structureof carbon fibers according to the present disclosure, a space may beprovided between the neighboring aggregates of the carbon fibers.According to the present disclosure, the density, at both side ends, ofthe aggregate of the carbon fibers differs at one side end and the otherside end. Therefore, the space is provided between the neighboringaggregates of the carbon fibers. As a result, the aggregate structure ofcarbon fibers according to the present disclosure enables the spacebetween the neighboring aggregates of the carbon fibers to beeffectively utilized. Further, in the aggregate structure of carbonfibers according to the present disclosure, a substance different fromthe carbon fibers may be provided between the neighboring aggregates ofthe carbon fibers. According to the present disclosure, the density, atboth side ends, of the aggregate of the carbon fibers differs at oneside end and the other side end. Hence, the substance different from thecarbon fibers can be provided between the neighboring aggregates of thecarbon fibers. As a result, the aggregate structure of carbon fibersaccording to the present disclosure enables the aggregate of the carbonfibers to be combined with the substance different from the carbonfibers.

The third embodiment will exemplify a method of how the spaces wherenone of the carbon nanotubes 1 exist are utilized. A scheme in the thirdembodiment is that dielectric films are formed in the spaces where noneof the carbon nanotubes 1 exist. Namely, the dielectric films are formedin the E-areas in FIG. 14. Thus, the dielectric films are formed in thespaces where none of the carbon nanotubes 1 exist, whereby the carbonnanotube group 5 having the different densities of the carbon nanotubes1 can be utilized as a reinforcing material for the strength of thedielectric film. For example, nanoporous silica functioning as thedielectric film is weak in its mechanical strength. Such being the case,the carbon nanotube group 5 having the different densities of the carbonnanotubes 1 is used as the reinforcing material for the strength of thedielectric film, thereby enabling the mechanical strength of thedielectric film to be reinforced.

Further, a plating metal may also be formed in the space where none ofthe carbon nanotubes 1 exist. Namely, a metallic layer may be formed inthe space where none of the carbon nanotubes 1 exist. Furthermore, theresin may also fill the space where none of the carbon nanotubes 1exist. For example, an organic substance is given as the resin thatfills the space where none of the carbon nanotubes 1 exist. Moreover, aninsulating film composed of SiO₂ etc may be formed in the space wherenone of the carbon nanotubes 1 exist.

Thus, the dielectric film, the metallic layer, the resin and theinsulating film are formed in the spaces where none of the carbonnanotubes 1 exist, thereby enabling a device characteristic, a heatradiation characteristic and a device strength to be improved. In theaggregate structure of carbon fibers according to the presentdisclosure, a substance different from the carbon fibers may be any oneof a dielectric body, an organic substance, a metal and an insulator.

Fourth Embodiment

An fourth embodiment of the present disclosure will be described withreference to the drawings in FIGS. 15 and 16. The fourth embodiment willexemplify a method of combining the carbon nanotube groups 5 having thedifferent densities of the carbon nanotubes 1, which are organizedaccording to the first embodiment or the second embodiment.

At the first onset, a plurality of carbon nanotube groups 5 having thedifferent densities of the carbon nanotubes 1 is disposed on the samestraight line. In this case, the carbon nanotube groups 5 are disposedso that the other side ends exhibiting the higher density than that ofone side ends are oriented in the same direction. As illustrated in FIG.15, the plurality of carbon nanotube groups 5 having the differentdensities of the carbon nanotubes 1 is disposed on the same straightline. Further, the other side ends exhibiting the higher density thanthat of one side ends are so disposed as to be oriented in the samedirection. Herein, with respect to the side ends of the carbon nanotubegroup 5, the other side end exhibiting the higher density of the carbonnanotube 1 than that of one side end, is called a high-density side end.

Next, the carbon nanotube group 5 having the different densities of thecarbon nanotubes 1 is further interposed between the plurality of carbonnanotube groups 5 having the different densities of the carbon nanotubes1 disposed on the same straight line. In this case, the carbon nanotubegroup 5 having the different densities of the carbon nanotubes 1 isfurther disposed so that the high-density side end is oriented in thedirection opposite to the high-density side ends of the plurality ofalready-arranged carbon nanotube groups 5 having the different densitiesof the carbon nanotubes 1. Namely, the pluralities of carbon nanotubegroups 5 having the different densities of the carbon nanotubes 1 aredisposed on the same straight lines so that the high-density side endsalternate with each other in their directions. FIG. 16 is a front viewshowing a case where the pluralities of carbon nanotube groups 5 havingthe different densities of the carbon nanotubes 1 are disposed on thesame straight lines so that the high-density side ends alternate witheach other in their directions.

The carbon nanotube group 5 having the different densities of the carbonnanotubes 1 is further disposed in the space where none of the carbonnanotubes 1 exist, whereby the density of the carbon nanotube groups 5can be increased. Namely, the high-density carbon nanotube groups 5 canbe organized. In the aggregate structure of carbon fibers according tothe present disclosure, the neighboring aggregates of the carbon fibersmay be aligned in different directions. According to the presentdisclosure, the density, at both side ends, of the aggregate of thecarbon fibers differs at one side end and the other side end. Therefore,the aggregate of the carbon fibers can be aligned in the differentdirections between the neighboring aggregates of the carbon fibers. As aresult, the aggregate structure of carbon fibers according to thepresent disclosure enables the aggregate of the carbon fibers and theaggregate of the carbon fibers aligned in the different direction to becombined.

Fifth Embodiment

A fifth embodiment of the present disclosure will hereinafter bedescribed with reference to the drawings in FIGS. 17 through 25. Thegrowth method of the carbon nanotubes 1 in the fifth embodiment will bedescribed with reference to the drawings in FIGS. 17 and 18. At first, acatalyst is deposited on a silicon substrate 7 with an oxide film. Inthis case, a particulated catalyst may also be used, and a film-likecatalyst deposited by the sputtering method may also be employed.

The fifth embodiment will be explained by using iron as the catalyst tobe deposited on the silicon substrate 7 with the oxide film. Moreover,the fifth embodiment will be described by using the sputtering method asthe method of depositing the iron catalyst on the silicon substrate 7with the oxide film. A iron film 8 having a thickness of 1 nm isdeposited by the sputtering method on the silicon substrate 7 with theoxide film, and undergoes patterning to obtain the iron film 8 that isapproximately 5 μm in diameter. FIG. 17 shows the post-patterning ironfilm 8. As illustrated in FIG. 17, the iron film 8 taking substantiallya circular shape is formed by the patterning on the silicon substrate 7with the oxide film. The diameter of the iron film 8 is given as anexemplification, and the present disclosure, without being limited tothis diameter, may involve patterning the iron film 8 in any size.

The silicon substrate 7 with the oxide film, on which thepost-patterning iron film 8 is formed, is placed on a heating stagewithin the normal thermal CVD furnace, and vacuum evacuation isconducted. Then, the silicon substrate 7 with the oxide film is heatedtill a temperature of the silicon substrate 7 with the oxide filmreaches 590° C. Thereafter, a mixture gas of argon (Ar) and acetylene(C2H2) is introduced into the thermal CVD furnace for 30 min. In thiscase, a pressure of the mixture gas of argon (Ar) and acetylene (C2H2)is set to 1 kPa. Thus, the vertically-aligned growth of the carbonnanotubes 1 on the silicon substrate 7 with the oxide film is attained.

FIG. 18 shows the carbon nanotube groups 5 grown in vertical alignmenton the silicon substrate 7 with the oxide film. Each individual carbonnanotube 1 is on the order of 10 nm in diameter and on the order of 20μm in length. Further, the density of the carbon nanotubes 1 of thecarbon nanotube group 5 is approximately 1E11 pieces/cm2. The density ofthe carbon nanotubes each having the diameter of 10 nm in a closestpacking state is approximately 1E12 piece/cm2, and therefore anoccupancy rate is merely 10%.

Next, a process of highly densifying the carbon nanotubes 1 of thecarbon nanotube group 5 will be described with reference to the drawingsin FIGS. 19 through 25. At first, the carbon nanotube group 5 is dippedinto a solvent 9. The solvent 9, into which the carbon nanotube group 5is dipped, involves using organic solvents such as DMF(N,N-dimethylformamide), dichloroethane, isopropyl alcohol, ethanol,methanol, and inorganic solvents such as water.

Specifically, the solvent 9 kept at a room temperature is poured into acontainer 10 in a size capable of accommodating the silicon substrate 7with the oxide film. Then, the silicon substrate 7 with the oxide filmis inserted vertically or laterally into the container 10 containing thesolvent 9, thus dipping the carbon nanotube groups 5 into the solvent 9.

FIGS. 19 through 21 are views showing a process of adhering the solvent9 to the carbon nanotube groups 5. In this process, the siliconsubstrate 7 with the oxide film is inserted laterally into the container10 containing the solvent 9 and is, after dipping the carbon nanotubegroups 5 into the solvent 9, pulled up from the container 10 containingthe solvent 9. To be specific, as illustrated in FIG. 19, the siliconsubstrate 7 with the oxide film is disposed laterally. Then, as shown inFIG. 20, the silicon substrate 7 with the oxide film is dipped into thecontainer 10 containing the solvent 9. In this case, the whole of thecarbon nanotube groups 5 are dipped into the solvent 9. Namely, thesolvent 9 is adhered to the whole of the carbon nanotube groups 5.

Next, after the carbon nanotube groups 5 have been dipped into thesolvent 9 for about one minute, as illustrated in FIG. 21, the carbonnanotube groups 5 are pulled out of the solvent 9. A period of time forwhich the carbon nanotube groups 5 are dipped into the solvent 9 is notlimited to one minute, however, the dipping time is properly adjusted,depending on a state of how much the solvent 9 is adhered to the carbonnanotube groups 5.

FIGS. 22 through 24 are views showing a process of adhering the solvent9 to the carbon nanotube groups 5. In this process, the siliconsubstrate 7 with the oxide film is inserted vertically into thecontainer 10 containing the solvent 9 and is, after dipping the carbonnanotube groups 5 into the solvent 9, pulled up from the container 10containing the solvent 9. To be specific, as illustrated in FIG. 22, thesilicon substrate 7 with the oxide film is disposed vertically. Then, asshown in FIG. 23, the silicon substrate 7 with the oxide film is dippedinto the container 10 containing the solvent 9. In this case, the wholeof the carbon nanotube groups 5 are dipped into the solvent 9. Namely,the solvent 9 is adhered to the whole of the carbon nanotube groups 5.

Next, after the carbon nanotube groups 5 have been dipped into thesolvent 9 for about one minute, as illustrated in FIG. 24, the carbonnanotube groups 5 are pulled out of the solvent 9. A period of time forwhich the carbon nanotube groups 5 are dipped into the solvent 9 is notlimited to one minute, however, the dipping time is properly adjusted,depending on a state of how much the solvent 9 is adhered to the carbonnanotube groups 5.

Moreover, if the adhering state of the solvent 9 to the carbon nanotubegroups 5 is not so well, the adhering state of the solvent 9 to thecarbon nanotube groups 5 is improved by adding, to the solvent 9,interfacial active agents such as SDS (Sodium Dodecyl Sulfate) orfunctional molecules such as pyrene, parylene, anthracene, porphyrin,phthalocyanine and DNA.

The fifth embodiment has exemplified the method of inserting the siliconsubstrate 7 with the oxide film into the container 10 containing thesolvent 9 and, after dipping the carbon nanotube groups 5 into thesolvent 9, pulling up the silicon substrate 7 with the oxide film out ofthe container 10 containing the solvent 9. The present disclosure isnot, however, limited to this method, and the solvent 9 may also beadhered to the carbon nanotube groups 5 by dropping the solvent 9 intothe carbon nanotube groups 5 by use of a spin coating method.

After adhering the solvent 9 to the carbon nanotube groups 5, the carbonnanotube groups 5 are dried. A method of drying the carbon nanotubegroups 5 may involve employing a method of naturally drying the carbonnanotube groups 5 and may involve using a method of quickly drying thecarbon nanotube groups 5 by heating the silicon substrate 7 with theoxide film to a temperature of approximately 200° C.

In the process of drying the carbon nanotube groups 5, the carbonnanotubes 1 provided at the distal end portions (the end portions of thecarbon nanotube groups 5, which do not abut on the silicon substrate 7with the oxide film) of the carbon nanotube groups 5 are attracted toeach other by dint of capillary attraction. The carbon nanotubes 1attracted to each other are tightly fitted to each other byintermolecular force. Therefore, as illustrated in FIG. 25, at thedistal end portions of the carbon nanotube groups 5, there occurs astate where the carbon nanotubes 1 lean on each other. Namely, thecarbon nanotube groups 5 are organized, in which the density of thecarbon nanotubes 1 at the distal end portions of the carbon nanotubegroups 5 is different from the density of the carbon nanotubes 1 at theproximal end portions of the carbon nanotube groups 5 (which are the endportions, abutting on the silicon substrate with the oxide film, of thecarbon nanotube groups 5).

The density of the carbon nanotubes 1 of the thus-organized differs atthe distal end portions and the proximal end portions of the carbonnanotube groups 5. Namely, there are organized the carbon nanotubegroups, in which the density of the carbon nanotubes 1 differs at oneside ends and the other side ends of the carbon nanotube groups 5. Thedensity of the carbon nanotubes 1 at the distal end portions of thecarbon nanotube groups 5 becomes higher than the density of the carbonnanotubes 1 at the proximal end portions of the carbon nanotube groups5. Accordingly, in the carbon nanotube groups 5 illustrated in FIG. 25,the density of the carbon nanotubes 1 at the distal end portions of thecarbon nanotube groups 5 is as high as the closest packing level.

Sixth Embodiment

A sixth embodiment of the present disclosure will be described withreference to the drawings in FIGS. 26 through 33. With respect to thecarbon nanotube groups 5 organized by the method described in the firstembodiment, the second embodiment or the fifth embodiment, the carbonnanotubes 1 provided at one side ends of the side ends of the carbonnanotube groups 5 have the high density. The sixth embodiment willexemplify a method of highly densifying the carbon nanotubes 1 providedat both side ends of the carbon nanotube groups 5. Explainedspecifically is a method of generating a state where the carbonnanotubes 1 at both side ends of the carbon nanotube groups 5 are soformed as to lean on each other, and the carbon nanotubes 1 of thecarbon nanotube groups 5 lean on each other on the whole.

At first, a substrate 20 on which the carbon nanotube groups 5 are grownis prepared. The sixth embodiment uses, as the substrate 20, the siliconsubstrate 2 exemplified in the first embodiment and the secondembodiment or the silicon substrate 7 with the oxide film exemplified inthe fifth embodiment. Herein, the process of increasing the density ofthe carbon nanotubes 1 of the carbon nanotube group 5, which has beenexplained in the first embodiment, the second embodiment or the fifthembodiment, is termed the densification process. Further, the carbonnanotube groups 5, in which the carbon nanotubes 1 of the carbonnanotube groups 5 are highly-densified, are referred to as thehighly-densified carbon nanotube groups 5. The carbon nanotube groups 5grown on the substrate 20 are subjected to the densification processexplained in the first embodiment, the second embodiment or the fifthembodiment, thereby highly densifying the carbon nanotubes 1 of thecarbon nanotube groups 5. FIG. 26 illustrates the highly-densifiedcarbon nanotube groups 5 and the substrate 20.

Next, as shown in FIG. 27, there is prepared a substrate 21 taking thesame size as that of the substrate 20 on which the carbon nanotubegroups 5 are grown. Then, a low-melting metal film 22 is deposited onthe surface of the substrate 21. For example, the low-melting metal film22 is solder, indium, etc. A thickness of the low-melting metal film 22deposited on the surface of the substrate 21 is set to severalmicrometers (μm). Thus, a substrate 23 with the low-melting metal filmis manufactured by depositing the low-melting metal film 22 on thesurface of the substrate 21.

Then, as shown in FIG. 28, the substrate 23 with the low-melting metalfilm and the substrate 20 are superposed on each other in a way thatinterposes the carbon nanotube groups 5 therebetween. Specifically, thesubstrate 23 with the low-melting metal film and the substrate 20 aresuperposed on each other so that the low-melting metal film 22 depositedon the surface of the substrate 21 abuts on the side ends (the side endsof the carbon nanotube groups 5, which do not abut on the substrate 20)of the carbon nanotube groups 5.

Then, the substrate 23 with the low-melting metal film is heated so thatthe temperature of the substrate 23 with the low-melting metal filmreaches the melting point or above of the low-melting metal film 22, andthereafter the substrate 23 with the low-melting metal film is cooled.After cooling the low-melting metal film 22, the substrate 23 with thelow-melting metal film and the substrate 20 are separated from eachother. In the case of separating the substrate 23 with the low-meltingmetal film and the substrate 20 from each other, there occurs a state inwhich the carbon nanotube groups 5 are tightly fitted to the substrate23 with the low-melting metal film. Namely, the carbon nanotube groups 5are peeled off the substrate 20 but tightly fitted to the substrate 23with the low-melting metal film. As shown in FIG. 29, the carbonnanotube groups 5 are peeled off the substrate 20 but tightly fitted tothe substrate 23 with the low-melting metal film.

If the tight-fitting between the substrate 20 and the carbon nanotubegroups 5 is strong, the carbon nanotube groups 5 are neither peeled offthe substrate 20 nor tightly fitted to the substrate 23 with thelow-melting metal film. In the first embodiment, the second embodimentand the fifth embodiment, the extremely thin catalyst layer (which isseveral nanometers (nm) or under in thickness) is deposited on thesilicon substrate 2 or the silicon substrate 7 with the oxide film, andthereafter the carbon nanotube groups 5 are grown thereon. In the sixthembodiment, the silicon substrate 2 or the silicon substrate 7 with theoxide film is used as the substrate 20. Accordingly, if the extremelythin catalyst layer is deposited on the substrate 20, the tight-fittingforce between the substrate 20 and the carbon nanotube groups 5 is weak.Therefore, such a problem does not arise that the carbon nanotube groups5 are not peeled off the substrate 20.

As shown in FIG. 29, the side ends, abutting on the substrate 23 withthe low-melting metal film, of the side ends of the carbon nanotubegroups 5 tightly fitted to the substrate 23 with the low-melting metalfilm have the higher density of the carbon nanotubes 1 than the densityof the other side ends (the side ends, not abutting on the substrate 23with the low-melting metal film, of the side ends of the carbon nanotubegroups 5). As the carbon nanotube groups 5 get distanced farther fromthe substrate 23 with the low-melting metal film, a horizontal width ofevery carbon nanotube group 5 expands. Namely, as the carbon nanotubegroups 5 get distanced farther from the substrate 23 with thelow-melting metal film, the carbon nanotubes 1 of the carbon nanotubegroups 5 have a lower density.

The densification process explained in the first embodiment, the secondembodiment or the fifth embodiment is executed on the substrate 23 withthe low-melting metal film, to which the high-density side ends of thecarbon nanotubes 1 are tightly fitted, in the both side ends of thecarbon nanotube groups 5. Namely, the densification process explained inthe first embodiment, the second embodiment or the fifth embodiment isexecuted on the low-density side ends of the carbon nanotubes 1 in theboth side ends of the carbon nanotube groups 5.

When the densification process is executed on the low-density side endsof the carbon nanotubes 1 in the both side ends of the carbon nanotubegroups 5, thereby organizing the carbon nanotube groups 5 in which thecarbon nanotubes 1 at both side ends of the carbon nanotube groups 5have the high densities.

FIG. 30 shows a process of dipping the carbon nanotube groups 5 tightlyfitted to the substrate 23 with the low-melting metal film into thecontainer 10 containing the solvent 9. FIG. 31 shows a process ofpulling up the carbon nanotube groups 5 tightly fitted to the substrate23 with the low-melting metal film from the container 10 containing thesolvent 9. The densities of the carbon nanotubes 1 at the both side endsof the carbon nanotube groups 5 illustrated in FIG. 31 are as high asthe closest packing level.

Moreover, in the case of utilizing low-melting metals (alloy) havingdifferent melting points, the highly-densified carbon nanotube groups 5can have a much higher density. A method of giving the much higherdensity to the carbon nanotube groups 5, in which the carbon nanotubes 1at the both side ends of the carbon nanotube groups 5 are highlydensified, will be described with reference to FIGS. 32 and 33.

As shown in FIG. 32, there is prepared the substrate 23 with thelow-melting metal film that is tightly fitted with the carbon nanotubegroups 5 in which the carbon nanotubes 1 at both side ends of the carbonnanotube groups 5 are highly densified, and a substrate 30 with thelow-melting metal film. The size of the substrate 23 with thelow-melting metal film is the same as that of the substrate 30 with thelow-melting metal film. The substrate 30 with the low-melting metal filmis constructed by depositing a low-melting metal film 32 on the surfaceof the substrate 31. For example, the low-melting metal film 32 issolder, indium, etc. In this case, the low-melting metal film 32 havingthe higher melting point than that of the low-melting metal film 22deposited on the substrate 30 with the low-melting metal film, isdeposited on the surface of the substrate 31. Further, the thickness ofthe low-melting metal film 32 deposited on the surface of the substrate31 is set to several micrometers (μm).

Next, as shown in FIG. 33, the substrate 23 with the low-melting metalfilm and the substrate 30 with the low-melting metal film are superposedon each other. Specifically, the substrate 23 with the low-melting metalfilm and the substrate 30 with the low-melting metal film are superposedon each other so that the side ends (the side ends, not abutting on thesubstrate 23 with the low-melting metal film, of the side ends of thecarbon nanotube groups 5) of the carbon nanotube groups 5 abut on thelow-melting metal film 32 deposited on the surface of the substrate 31.

Then, the substrate 23 with the low-melting metal film and the substrate30 with the low-melting metal film are heated so that a temperature ofthe substrate 23 with the low-melting metal film and a temperature ofthe substrate 30 with the low-melting metal film are equal to or higherthan the melting point of the low-melting metal film 32. Thereafter, thesubstrate 23 with the low-melting metal film and the substrate 30 withthe low-melting metal film are cooled. In this case, the substrate 23and the substrate 30 are cooled so that the temperature of the substrate23 with the low-melting metal film and the temperature of the substrate30 with the low-melting metal film are equal to or higher than themelting point of the low-melting metal film 22 but equal to or lowerthan the melting point of the low-melting metal film 32.

Then, the substrate 23 with the low-melting metal film and the substrate30 with the low-melting metal film are separated from each other. Whenthe substrate 23 with the low-melting metal film and the substrate 30with the low-melting metal film are separated from each other, thereoccurs a state where the carbon nanotube groups 5 are tightly fitted tothe substrate 30 with the low-melting metal film. Namely, the carbonnanotube groups 5 are peeled off the substrate 23 with the low-meltingmetal film but are tightly fitted to the substrate 30 with thelow-melting metal film.

When equal to or higher than the melting point of the low-melting metalfilm 22 but equal to or lower than the melting point of the low-meltingmetal film 32, the low-melting metal film 22 deposited on the substrate23 with the low-melting metal film is in a melting state. Therefore, thetight-fitting between the carbon nanotube groups 5 and the substrate 30with the low-melting metal film is stronger than the tight-fittingbetween the carbon nanotube groups 5 and the substrate 23 with thelow-melting metal film. Accordingly, the carbon nanotube groups 5 arepeeled off the substrate 23 with the low-melting metal film but tightlyfitted to the substrate 30 with the low-melting metal film.

Then, the carbon nanotube groups 5 bonded to the substrate 30 with thelow-melting metal film undergo the densification process explained inthe first embodiment, the second embodiment or the fifth embodiment,whereby the carbon nanotubes 1 of the carbon nanotube groups 5 can befurther highly densified. This process can be repeated a plural numberof times, and the density of the carbon nanotubes 1 of the carbonnanotube groups 5 can be made much higher.

According to the sixth embodiment, the carbon nanotubes 1 of the carbonnanotube groups 5 can be highly densified throughout the carbon nanotubegroups 5.

Seventh Embodiment

A seventh embodiment of the present disclosure will be described withreference to the drawings in FIGS. 34 through 43. The seventh embodimentwill exemplify a method of applying, to a heat radiation bump, thecarbon nanotube groups 5 highly densified by the densification processexplained in the first embodiment, the second embodiment or the fifthembodiment.

A face-up structure of joining a high-power transistor chip 40 directlyto a package 41 has hitherto been employed. FIG. 34 illustratesconventional transistor packaging. The high-power transistor chip 40 andthe package 41 are connected by wire-bonding. To be specific, electrodes42 formed on the surface of the high-power transistor chip 40 areconnected to electrodes (unillustrated) formed on the package 41 bywires such as gold wires. The transistor packaging illustrated in FIG.34 uses the face-up structure and ensures a heat radiation property byradiating the heat via the high-power transistor chip 40.

Moreover, flip-chip packaging is that the high-power transistor chip 40is reversed, and the electrodes 42 formed on the surface of thehigh-power transistor chip 40 are connected to the electrodes on thepackage 41 by carbon nanotube bumps 43. As illustrated in FIG. 35, theflip-chip packaging is that the electrodes 42 formed on the surface ofthe high-power transistor chip 40 are connected to the electrodes(unillustrated) formed on the surface of the package 41 by reversing thehigh-power transistor chip 40. Namely, with the surface of thehigh-power transistor chip 40 being directed to the package 41, theelectrodes 42 formed on the surface of the high-power transistor chip 40are connected to the electrodes formed on the package 41. Herein, thebump is a terminal formed in a protruded shape. The carbon nanotubebumps 43 are the terminals provided by forming the carbon nanotubegroups 5 in the protruded shapes.

As illustrated in FIG. 36, the carbon nanotube bumps 43 connect theelectrodes 42 (unillustrated) formed on the surface of the high-powertransistor chip 40 to the electrodes formed on the package 41. In FIG.36, the high-power transistor chip 40 is reversed, and the electrodes 42(unillustrated) formed on the surface of the high-power transistor chip40 are directed to the package 41. Further, the carbon nanotube bumps 43have a role of heat radiation paths for radiating the heat generated bythe high-power transistor chip 40. The sufficient radiation of the heatgenerated by the high-power transistor chip 40 entails increasing thedensity of the carbon nanotubes 1 of the carbon nanotube bumps 43. Theoccupancy rate of the carbon nanotubes 1 of the conventional carbonnanotube bumps 43 is on the order of 10%, and hence the density of thecarbon nanotubes 1 of the conventional carbon nanotube bumps 43 has beendesired to be increased.

The seventh embodiment applies, to the carbon nanotube bumps 43, thecarbon nanotube groups 5 highly densified by the densification processexplained in the first embodiment, the second embodiment or the fifthembodiment. To be specific, the electrodes 42 formed on the surface ofthe high-power transistor chip 40 are connected to the electrodes formedon the package 41 by employing the highly-densified carbon nanotubegroups 5 as the carbon nanotube bumps 43. Moreover, in the seventhembodiment, the substrate on which the carbon nanotubes 1 are growninvolves using an aluminum nitride substrate 50. The aluminum nitridesubstrate 50 is used as a material for manufacturing the package 41. Thealuminum nitride substrate 50 used as the substrate on which the carbonnanotubes 1 are grown are an exemplification, and the present disclosureis not limited to this substrate.

As shown in FIG. 37, electrodes 51 are each formed of a metal such asgold on the aluminum nitride substrate 50. Aluminum is deposited up to athickness of 5 nm on the electrodes 51. Then, iron is deposited up to athickness of 1 nm on aluminum deposited on the electrodes 51. In thiscase, aluminum and iron are used as catalysts for growing the carbonnanotubes 1.

Aluminum deposited on the electrodes 51 and iron deposited on aluminumundergo patterning. In this case, patterning shapes of aluminum and ironare set the same as the shape of the electrodes 42 formed on the surfaceof the high-power transistor chip 40. Further, central positions ofaluminum and iron shaped by the patterning are set the same as thecentral positions of the electrodes 42 formed on the surface of thehigh-power transistor chip 40. Sizes of aluminum and iron shaped by thepatterning may be the same as or several times as large as the size ofthe electrodes 42 formed on the surface of the high-power transistorchip 40.

Next, the carbon nanotube groups 5 each having a length equal to orlonger than 20 μm are grown on the aluminum nitride substrate 50 by useof the method explained in the first embodiment or the fifth embodiment.FIG. 38 illustrates the carbon nanotube groups 5 grown on the aluminumnitride substrate 50. The occupancy rate of the carbon nanotubes 1 ofthe carbon nanotube groups 5 shown in FIG. 38 is approximately 10%.

Then, the carbon nanotubes 1 at the side ends of the carbon nanotubegroups 5, which do not abut on the aluminum nitride substrate 50, arehighly densified by use of the densification process described in thefirst embodiment, the second embodiment or the fifth embodiment. In thiscase, the carbon nanotube groups 5 are grown so that a size of thediameter of the side ends of the highly-densified carbon nanotubes 1 inthe side ends of the carbon nanotube groups 5, is set the same as thesize of the electrodes 42 on the high-power transistor chip 40 or setsmaller than the size of the electrodes 42 on the high-power transistorchip 40.

A size of the catalyst deposited on the aluminum nitride substrate 50can be changed, thereby it is possible to change the size of thediameter of the side ends of the highly-densified carbon nanotubes 1 inthe side ends of the carbon nanotube groups 5. Accordingly, on theoccasion of patterning the catalyst deposited on the aluminum nitridesubstrate 50 on which the carbon nanotube groups 5 are grown, the sizeof the catalyst is changed by taking into consideration the size of theelectrodes 42 on the high-power transistor chip 40. A relationshipbetween the size of the catalyst deposited on the aluminum nitridesubstrate 50 and the size of the diameter of the side ends of thehighly-densified carbon nanotubes 1 in the side ends of the carbonnanotube groups 5, maybe obtained empirically or in simulation.

FIG. 39 shows the highly-densified carbon nanotube groups 5 and thealuminum nitride substrate 50. In the carbon nanotube groups 5 organizedby the method described in the first embodiment, the second embodimentor the fifth embodiment, the carbon nanotubes 1 have different lengths.To be specific, there is a high possibility that the carbon nanotubegroups 5 are grown with irregularity in the lengths of the carbonnanotubes 1. If the irregularity in the lengths of the respective carbonnanotubes 1 of the carbon nanotube groups 5 is large, a process ofequalizing the lengths of the carbon nanotubes 1 of the carbon nanotubegroups 5 is carried out.

The process of equalizing the lengths of the carbon nanotubes 1 of thecarbon nanotube groups 5 will be described with reference to FIGS. 40through 43. As illustrated in FIG. 40, the carbon nanotube groups 5grown on the aluminum nitride substrate 50 are not uniform in terms ofthe lengths of the carbon nanotubes 1. The carbon nanotube groups 5shown in FIG. 40 are subjected to the densification process described inthe first embodiment, the second embodiment or the fifth embodiment.

To begin with, an interlayer insulating film 60 is deposited on thealuminum nitride substrate 50 in a way that covers the carbon nanotubegroups 5. The interlayer insulating film 60 involves using a poroussilica film, an SOG (Spin On Glass) film, etc. After depositing theinterlayer insulating film 60 on the aluminum nitride substrate 50, theinterlayer insulating film 60 is solidified by heating the aluminumnitride substrate 50 and the interlayer insulating film 60. FIG. 41 is aview showing a structure of the aluminum nitride substrate 50 on whichthe interlayer insulating film 60 is deposited so as to cover the carbonnanotube groups 5.

The interlayer insulating film 60 is deposited on the aluminum nitridesubstrate 50, and, when executing a heating treatment, the carbonnanotube groups 5 are hardened together with the interlayer insulatingfilm 60. After the carbon nanotube groups 5 have been hardened togetherwith the interlayer insulating film 60, the carbon nanotube groups 5 andthe interlayer insulating film 60 are polished by a chemical mechanicalpolishing (CMP) process. In this case, the carbon nanotube groups 5 andthe interlayer insulating film 60 are polished till the lengths of thecarbon nanotubes 1 of the carbon nanotube groups 5 get uniform. FIG. 42illustrates the aluminum nitride substrate 50 after the carbon nanotubegroups 5 and the interlayer insulating film 60 have been polished.

Thereafter, the interlayer insulating film 60 deposited on the aluminumnitride substrate 50 is removed. If unnecessary for removing theinterlayer insulating film 60 deposited on the aluminum nitridesubstrate 50, the interlayer insulating film 60 deposited on thealuminum nitride substrate 50 may not be removed.

Thus, the lengths of the carbon nanotubes 1 of the carbon nanotubegroups 5 are equalized, thereby enabling the carbon nanotube groups 5 tobe stably bonded to the high-power transistor chip 40.

Given next is a description of a method of connecting the electrodes 42formed on the surface of the high-power transistor chip 40 to theelectrodes formed on the package 41 by employing the carbon nanotubegroups 5 as the carbon nanotube bumps 43.

To start with, the aluminum nitride substrate 50 utilized formanufacturing the package 41 is prepared. The carbon nanotube groups 5are grown on the aluminum nitride substrate 50 by the growth method ofthe carbon nanotube groups 5, which has been explained in the firstembodiment or the second embodiment. The carbon nanotube groups 5 formedon the aluminum nitride substrate 50 are subjected to the densificationprocess described in the first embodiment, the second embodiment or thefifth embodiment. Moreover, the carbon nanotube groups 5 formed on thealuminum nitride substrate 50 may also be subjected to the process ofequalizing the lengths of the carbon nanotubes 1.

Next, gold is deposited up to a thickness of 1 μm on the carbon nanotubegroups 5 formed on the aluminum nitride substrate 50. The thickness ofgold deposited on the carbon nanotube groups 5 is an exemplification,and the present disclosure is not limited to this thickness. Moreover,in the carbon nanotube groups 5 formed on the aluminum nitride substrate50, gold may be deposited on portions desired to be bonded to theelectrodes 42 formed on the surface of the high-power transistor chip40.

Then, the gold-deposited carbon nanotube groups 5 are bonded to theelectrodes 42 formed on the surface of the high-power transistor chip 40by use of a normal flip-chip bonder. The carbon nanotube groups 5 arebonded to the electrodes 42 formed on the surface of the high-powertransistor chip 40 under a pressure of 6 kg/cm2 at a temperature of345°. The pressure and the temperature are exemplifications, and thepresent disclosure is not limited to these values.

FIG. 43 is a view showing a structure of the aluminum nitride substrate50 provided with the high-power transistor chip 40. In FIG. 43, thecarbon nanotube groups 5 are employed as the carbon nanotube bumps 43.The electrodes 42 formed on the surface of the high-power transistorchip 40 are connected to electrodes 51 on the aluminum nitride substrate50 via the carbon nanotube groups 5. The carbon nanotubes 1 at the sideends, bonded to the high-power transistor chip 40, of the side ends ofthe carbon nanotube groups 5, have a 10-fold density as high as thedensity of the carbon nanotubes 1 at the side ends that are not bondedto the high-power transistor chip 40. Therefore, the carbon nanotubebumps 43 have the higher heat radiation property than the conventionalcarbon nanotube bumps 43 have. The highly-densified side ends of thecarbon nanotubes 1 in the side ends of the carbon nanotube groups 5 arebonded to the electrodes 42 formed on the high-power transistor chip 40,whereby the heat of the high-power transistor chip 40 is radiated viathe carbon nanotube groups 5.

Moreover, the electrodes 42 formed on the surface of the high-powertransistor chip 40 can be also connected to the electrodes 51 on thealuminum nitride substrate 50 by use of the carbon nanotube groups 5including the highly-densified carbon nanotubes 1 throughout. The carbonnanotube groups 5 including the highly-densified carbon nanotubes 1throughout can be manufactured by the method explained in the sixthembodiment. A degree of freedom of a design of the substrate for wiringcan be expanded by use of the carbon nanotube groups 5 including thehighly-densified carbon nanotubes 1 throughout.

Eighth Embodiment

An eighth embodiment of the present disclosure will be described withreference to the drawings in FIGS. 44 through 51. At the present, wiringfor an LSI is multi-layered wiring such as 10- or more-layered wiring,and copper is normally used as the wiring material. As a current densityincreases accompanying a decrease in wiring width of the LSI, an anxietyis disconnection due to electromigration. Therefore, one scheme is thatthe vertical wiring (via wiring) for the LSI is replaced with the carbonnanotubes 1 endurable against a much higher current density. FIG. 44illustrates a structure of LSI 70. As illustrated in FIG. 44, the LSI 70is constructed of insulating films 72 in between a copper wiring 71 isinterposed and vias 73 each electrically connecting the copper wiring 71to another copper wiring 71.

The eighth embodiment will exemplify a method of applying, to the LSIwiring, the carbon nanotube groups 5 that are highly densified by thedensification process described in the first embodiment, the secondembodiment or the fifth embodiment. In the eighth embodiment, the vias73 building up the LSI 70 shown in FIG. 44 are replaced with thehighly-densified carbon nanotube groups 5. A method of replacing thevias 73 building up the LSI 70 with the highly-densified carbon nanotubegroups 5, will be described with reference to the drawings in FIGS. 45through 51.

At the first onset, as illustrated in FIG. 45, a substrate 74 on whichthe carbon nanotube groups 5 are grown is prepared. In this case, thesilicon substrate 2 or the silicon substrate 7 with the oxide film mayalso be used as the substrate 74, and another substrate may also beavailable. The carbon nanotube groups 5 are grown on the substrate 74 byemploying the growth method of the carbon nanotubes 1, which is shown inthe first embodiment or the fifth embodiment. Moreover, the carbonnanotube groups 5 are highly densified by the densification processdescribed in the first embodiment, the second embodiment or the fifthembodiment. In the eighth embodiment, a catalyst for growing the carbonnanotube groups 5 on the substrate 74 involves using cobalt, iron andother metals.

It is required that the carbon nanotube groups 5 be grown on thesubstrate 74 for enabling the carbon nanotube groups 5 to be disposed inpositions of the vias 73 building up the LSI 70. Hence, in the eighthembodiment, the catalyst undergoes patterning so as to enable the carbonnanotube groups 5 to be disposed in the positions of the vias 73building up the LSI 70, and the carbon nanotube groups 5 are grown onthe substrate 74.

Next, a cobalt film 77 is deposited up to a thickness of 5 nm onelectrodes 76 of the LSI substrate 75, then a tantalum film 78 isdeposited up to a thickness of 5 nm on the cobalt film 77, and atitanium film 79 is deposited up to a thickness of 5 nm on the tantalumfilm 78. Note that an iron film, a nickel film, etc may also be used asa substitute for the cobalt film 77. Further, the cobalt film 77 mayalso be replaced with a film composed of a cobalt alloy, an iron alloyor a nickel alloy.

The substrate 74 is superposed on the LSI substrate 75 on which thecobalt film 77, the tantalum film 78 and the titanium film 79 aredeposited. Specifically, as shown in FIG. 46, the substrate 74 and theLSI substrate 75 are superposed on each other so that the side ends (theside ends, not abutting on the substrate 74, of the side ends of thecarbon nanotube groups 5) of the carbon nanotube groups 5 are broughtinto contact with the electrodes 76 of the LSI substrate 75. In thiscase, the substrate 74 and the LSI substrate 75 are superposed on eachother so that a longitudinal direction of the substrate 74 becomessubstantially parallel with a longitudinal direction of the LSIsubstrate 75. Moreover, the substrate 74 and the LSI substrate 75 aresuperposed on each other by optical alignment so that the side ends ofthe carbon nanotube groups 5 abut on the electrodes 76 of the LSIsubstrate 75.

The substrate 74 and the LSI substrate 75 in the state of beingsuperposed on each other are carried into the CVD furnace. The vacuumevacuation is conducted within the CVD furnace, and thereafter the stageon which the substrate 74 and the LSI substrate 75 are placed is heated.Then, after a temperature within the CVD furnace has been stabilized, aprocess gas (mixture gas) is introduced under 1 kPa into the CVDfurnace. In the eighth embodiment, the process gas involves using argon(Ar) and acetylene (C2H2). A hydrocarbon gas such as methane (CH4) andethylene (C2H4) or alcohol may be added to the process gas of argon (Ar)and acetylene (C2H2). Further, the hydrocarbon gas such as methane (CH4)and ethylene (C2H4) or alcohol may be used in place of acetylene (C2H4)in the process gas. Moreover, the process gas may consist of pluraltypes of hydrocarbon gasses and may also consist of the plural types ofhydrocarbon gasses and alcohol.

The process gas is introduced into the CVD furnace, whereby the cobaltfilm 77 deposited on the electrodes 76 of the LSI substrate 75 comes toa melting state. Therefore, the carbon nanotube groups 5 are firmlyjoined to the electrodes 76 of the LSI substrate 75.

A temperature of the stage within the CVD furnace is desirably atemperature (e.g., a temperature of 350° C.) of such a degree thatthough reacting on the cobalt film 77 and the process gas, the carbonnanotubes 1 of the carbon nanotube groups 5 are not grown. Note that thetemperature of the stage within the CVD furnace can fluctuate dependingon the type of the process gas and the thickness of the film depositedon the LSI substrate 75.

After joining the carbon nanotube groups 5 to the electrodes 76 of theLSI substrate 75, the substrate 74 and the LSI substrate 75 are takenout of the CVD furnace. Then, the substrate 74 and the LSI substrate 75are separated from each other. In the case of separating the substrate74 and the LSI substrate 75 from each other, there occurs a state inwhich the carbon nanotube groups 5 are tightly fitted to the electrodes76 of the LSI substrate 75. Namely, the carbon nanotube groups 5 arepeeled off the substrate 74 but are tightly fitted to the electrodes 76of the LSI substrate 75.

In the eighth embodiment, the carbon nanotube groups 5 are grown on thesubstrate 74 by use of the growth method of the carbon nanotubes 1explained in the first embodiment or the fifth embodiment. To bespecific, an extremely thin catalyst layer (which is several nanometers(nm) or under in thickness) is deposited on the substrate 74, andthereafter the carbon nanotube groups 5 are grown thereon. The extremelythin catalyst layer is deposited on the substrate 74, and hence thetight-fitting force between the substrate 74 and the carbon nanotubegroups 5 is weak. Therefore, such a problem does not arise that thecarbon nanotube groups 5 are not peeled off the substrate 74.

Further, as shown in FIG. 47, a gap between the substrate 74 and the LSIsubstrate 75 is filled with an interlayer insulating film 80 such as theSOG film or the porous silica film, and thereafter the substrate 74 andthe LSI substrate 75 may be separated. In this case, the interlayerinsulating film 80 is dissolved in a proper solvent, thus setting theinterlayer insulating film 80 in a liquid state.

Then, the substrate 74 and the LSI substrate 75 are dipped in the liquidinterlayer insulating film 80, thereby filling the gap between thesubstrate 74 and the LSI substrate 75 with the interlayer insulatingfilm 80. Further, in place of this scheme, the liquid interlayerinsulating film 80 is instilled in the gap between the substrate 74 andthe LSI substrate 75, thus filling the gap between the substrate 74 andthe LSI substrate 75 with the interlayer insulating film 80.

Then, the substrate 74 and the LSI substrate 75 are subjected to thethermal treatment, thereby solidifying the interlayer insulating film 80and forming the interlayer insulating film 80 between the substrate 74and the LSI substrate 75.

If the substrate 74 and the LSI substrate 75 are separated from eachother before forming the interlayer insulating film 80 in the gapbetween the substrate 74 and the LSI substrate 75, the interlayerinsulating film 80 is formed with respect to the LSI substrate 75 towhich the carbon nanotube groups 5 are tightly fitted. Specifically, theliquid interlayer insulating film 80 is applied over the LSI substrate75 to which the carbon nanotube groups 5 are tightly fitted by makinguse of the spin coating, thereby forming the interlayer insulating film80 with respect to the LSI substrate 75.

Further, after forming the interlayer insulating film 80 on thesubstrate 74, the substrate 74 and the LSI substrate 75 may besuperposed on each other. Namely, the substrate 74 and the LSI substrate75 are superposed on each other by use of the substrate 74 on which theinterlayer insulating film 80 has already be formed. In this case, theinterlayer insulating film 80 is formed on the substrate 74 by thefollowing method.

To begin with, the interlayer insulating film 80 is deposited on thesubstrate 74 in a way that covers the carbon nanotube groups 5. Afterdepositing the interlayer insulating film 80 on the substrate 74, theheating treatment is conducted, and the interlayer insulating film 80 isthus solidified. FIG. 48 is a view showing a structure of the substrate74 on which the interlayer insulating film 80 is deposited in a way thatcovers the carbon nanotube groups 5. The interlayer insulating film 80is deposited on the substrate 74, and the heating treatment is carriedout, whereby the carbon nanotube groups 5 are solidified together withthe interlayer insulating film 80. Thus, the interlayer insulating film80 is formed on the substrate 74.

Moreover, after the carbon nanotube groups 5 have been solidifiedtogether with the interlayer insulating film 80, the interlayerinsulating film 80 is polished by the chemical mechanical polishing(CMP) process. In this case, the interlayer insulating film 80 ispolished so that the distal ends of the carbon nanotube groups 5 getexposed. Furthermore, if the lengths of the carbon nanotubes 1 of thecarbon nanotube groups 5 are not uniform, the carbon nanotube groups 5and the interlayer insulating film 80 may also be polished till thelengths of the carbon nanotubes 1 of the carbon nanotube groups 5 areequalized.

Moreover, in the case of superposing the substrate 74 and the LSIsubstrate 75 by using the substrate 74 on which the interlayerinsulating film 80 has already been formed, the distal ends of thecarbon nanotube groups 5 may be protruded. Namely, as illustrated inFIG. 49, the length of the carbon nanotube group 5 is set larger than athicknesswise length of the interlayer insulating film 80 formed on thesubstrate 74. To be specific, the interlayer insulating film 80 iswet-etched or dry-etched, thus cutting only the interlayer insulatingfilm 80. The distal ends of the carbon nanotube groups 5 can beprotruded by cutting only the interlayer insulating film 80.

The wet etching in the eighth embodiment involves using liquid or gasdilute hydrogen fluoride. In the case of employing the porous silicafilm as the interlayer insulating film 80, if the wet etching isperformed, only the interlayer insulating film 80 is etched. Therefore,the distal ends of the carbon nanotube groups 5 can be protruded. In thecase of cutting the interlayer insulating film 80 by the dry etching,argon ions impinge on the interlayer insulating film 80 by thesputtering method. When executing the dry etching, only the interlayerinsulating film 80 is etched. Therefore, the distal ends of the carbonnanotube groups 5 can be protruded.

Thus, after forming the interlayer insulating film 80 on the substrate74, the substrate 74 and the LSI substrate 75 are superposed on eachother and then separated from each other, whereby the interlayerinsulating film 80 is formed on the LSI substrate 75, and there occurs astate in which the carbon nanotube groups 5 are tightly fitted to theLSI substrate 75.

Next, the LSI substrate 75 formed with the interlayer insulating film 80is subjected to the chemical mechanical polishing (CMP) process, and thecarbon nanotube groups 5 and the interlayer insulating film 80 arepolished till the length of the carbon nanotube group 5 and thethickness of the interlayer insulating film 80 reach desired ranges. TheLSI substrate 75 formed with the interlayer insulating film 80 may alsobe an LSI substrate 75 that is formed with the interlayer insulatingfilm 80 after separating the substrate 74 and the LSI substrate 75 fromeach other, and may also be an LSI substrate 75 that is formed with theinterlayer insulating film 80 before separating the substrate 74 and theLSI substrate 75 from each other. FIG. 50 illustrates the LSI substrate75 after polishing the carbon nanotube groups 5 and the interlayerinsulating film 80.

Next, copper wiring 71 is formed on the LSI substrate 75. To bespecific, copper is deposited on the carbon nanotube groups 5 tightlyfitted to the LSI substrate 75, and further deposited on the interlayerinsulating film 80 formed on the LSI substrate 75. Then, the depositedcopper undergoes patterning, and the copper wiring 71 is thus formed onthe LSI substrate 75. The interlayer insulating film 80 is formedbetween the copper wiring 71 and another copper wiring 71. Theinterlayer insulating film 80 may not be, however, formed at this stage.FIG. 51 illustrates the LSI substrate 75 after forming the copper wiring71.

A first wiring process is a process of forming the carbon nanotubegroups 5 and the interlayer insulating film 80 on the LSI substrate 75,and forming the copper wiring 71 on the carbon nanotube groups 5 and onthe interlayer insulating film 80. After executing the first wiringprocess, the carbon nanotube groups 5 are further formed on the LSIsubstrate 75. Namely, the carbon nanotube groups 5 are formed on thecopper wiring 71, thereby obtaining the multi-layered LSI substrate 75.A process of forming the carbon nanotube groups 5 on the copper wiring71 will hereinafter be described.

As shown in FIG. 52, the substrate 74, on which the carbon nanotubegroups 5 are grown, is prepared. The process of highly densifying thecarbon nanotube groups 5 grown on the substrate 74 is the same as thefirst wiring process. Further, the process of patterning the catalyst sothat the carbon nanotube groups 5 can be disposed in the positions ofthe vias 73 building up the LSI substrate 75 and growing the carbonnanotube groups 5 on the substrate 74, is the same as the first wiringprocess. Moreover, the process of patterning the catalyst so that thecarbon nanotube groups 5 can be disposed in the positions of the vias 73building up the LSI 70 and growing the carbon nanotube groups 5 on thesubstrate 74, is the same as the first wiring process.

Next, the cobalt film 77 is deposited up to a thickness of 5 nm on thecopper wiring 71, the tantalum film 78 is deposited up to a thickness of5 nm on the cobalt film 77, and the titan film 79 is deposited up to athickness of 5 nm on the tantalum film 78. Incidentally, the filmcomposed of iron, nickel, etc may be used as a substitute for the cobaltfilm 77.

Then, the LSI substrate 75 formed with the copper wiring 71 and thesubstrate 74 are superposed on each other. To be specific, asillustrated in FIG. 53, the substrate 74 and the LSI substrate 75 aresuperposed on each other so that the side ends of the carbon nanotubegroups 5, which do not abut on the substrate 74, are brought intocontact with the copper wiring 71. In this case, the substrate 74 andthe LSI substrate 75 are superposed on each other so that thelongitudinal direction of the substrate 74 becomes substantiallyparallel with the longitudinal direction of the LSI substrate 75.Moreover, the substrate 74 and the LSI substrate 75 are superposed oneach other by the optical alignment so that the side ends of the carbonnanotube groups 5 abut on the electrodes 76 of the LSI substrate 75.

Herein, the method of joining, to the copper wiring 71, the side ends(the side ends, not abutting on the substrate 74, of the carbon nanotubegroups 5) of the carbon nanotube groups 5, is the same as the method ofjoining the side ends of the carbon nanotube groups 5 to the electrodes76 in the first wiring process.

Then, after the gaps between the substrate 74 and the copper wiring 71has been filled with the interlayer insulating film 80, the substrate 74and the LSI substrate 75 are separated from each other. When thesubstrate 74 and the LSI substrate 75 are separated from each other,there occurs a state where the carbon nanotube groups 5 and the copperwiring 71 are tightly fitted to each other. Namely, the carbon nanotubegroups 5 are peeled off the substrate 74 but tightly fitted to thecopper wiring 71. FIG. 54 shows a state in which the carbon nanotubegroups 5 are peeled off the substrate 74 but tightly fitted to thecopper wiring 71 formed on the LSI substrate 75.

Next, the LSI substrate 75 formed with the interlayer insulating film 80is subjected to the chemical mechanical polishing (CMP) process, and thecarbon nanotube groups 5 and the interlayer insulating film 80 arepolished till the length of the carbon nanotube group 5 and thethickness of the interlayer insulating film 80 reach the desired ranges.FIG. 55 illustrates the LSI substrate 75 after polishing the carbonnanotube groups 5 and the interlayer insulating film 80.

Then, the copper wiring 71 is formed on the LSI substrate 75. The methodof forming the copper wiring 71 on the LSI substrate 75 is the same asthe first wiring process. A second wiring process is a process offorming the carbon nanotube groups 5 and the interlayer insulating film80 on the copper wiring 71, and further forming the copper wiring 71.The material and the method used for the first wiring process can beemployed for the second wiring process.

In the eighth embodiment, there is executed the first wiring process offorming the carbon nanotube groups 5 and the interlayer insulating film80 on the LSI substrate 75, and forming the copper wiring 71 on thecarbon nanotube groups 5 and on the interlayer insulating film 80. Then,according to the eighth embodiment, there is executed the second wiringprocess of forming the carbon nanotube groups 5 and the interlayerinsulating film 80 on the copper wiring 71, and further forming thecopper wiring 71. The multi-layered LSI using the carbon nanotube groups5 is organized by repeating the second wiring process.

Further, the method of bonding the carbon nanotube groups 5 to theelectrodes 76 or the copper wiring 71 by employing the cobalt film 77,the tantalum film 78 and the titanium film 79 in the eighth embodiment,can be applied to the seventh embodiment. Namely, the carbon nanotubegroups 5 may be bonded to the electrodes formed on the surface of thehigh-power transistor chip 40 in the seventh embodiment by making use ofthe method of bonding the carbon nanotube groups 5 to the electrodes 76in the eighth embodiment.

According to the eighth embodiment, the vias 73 building up the LSI 70are replaced with the highly-densified carbon nanotube groups 5, therebyenabling the possibility of the disconnection due to theelectromigration to be reduced. Namely, it is feasible to reduce thepossibility of the disconnection between the electrodes 76 building upthe LSI 70 and the copper wiring 71. Even when a current density rises,it is possible to reduce a possibility of disconnection between theelectrodes and the conductive material.

Modified Example

In the first embodiment through the eighth embodiment, a carbonnanofiber may be employed in place of the carbon nanotube 1. A growthmethod of the carbon nanofiber is the same as the growth method of thecarbon nanotube 1, and its description is herein omitted. Further, thestructures and the methods in the first embodiment through the eighthembodiment of the present disclosure can be applied to hyperfineline-shaped substances such as the carbon nanotubes 1 and the carbonnanofibers. Moreover, the structures and the methods in the firstembodiment through the eighth embodiment of the present disclosure canbe applied to carbon fibers. Still further, the structures and themethods in the first embodiment through the eighth embodiment of thepresent disclosure can be applied to hollowed carbon fibers andnon-hollowed carbon fibers. In the aggregate structure of carbon fibersaccording to the present disclosure, the carbon fibers may be hollowed.

1.-8. (canceled)
 9. A method of manufacturing an aggregate structure ofcarbon fibers, comprising: a step of growing an aggregate of the carbonfibers aligned in a lengthwise direction substantially in a verticaldirection from a substrate surface; and a densifying step of densifyingthe carbon fibers at one side end of the aggregate of the carbon fibersin the lengthwise direction.
 10. The method of manufacturing anaggregate structure of carbon fibers according to claim 9, wherein thedensifying step includes: a step of making a solvent containing anadhesive substance different from the carbon fibers permeate through theaggregate of the carbon fibers; and a step of evaporating the solvent.11. The method of manufacturing an aggregate structure of carbon fibersaccording to claim 9, wherein the densifying step includes: a step ofmaking a solvent permeate through the aggregate of the carbon fibers;and a step of drying the aggregate of the carbon fibers and the solvent.12. A method of manufacturing an aggregate structure of carbon fibers,comprising: a step of growing an aggregate of the carbon fibers alignedin a lengthwise direction substantially in a vertical direction from asubstrate surface of a first substrate; a densifying step of densifyingone side ends of the aggregate of the carbon fibers in the lengthwisedirection; a step of tightly fitting the other side ends of theaggregate of the carbon fibers in the lengthwise direction to asubstrate surface of a second substrate; a step of peeling the aggregateof the carbon fibers grown on the substrate surface of the firstsubstrate from the substrate surface of the first substrate; and adensifying step of densifying the other side ends of the aggregate ofthe carbon fibers in the lengthwise direction.
 13. The method ofmanufacturing an aggregate structure of carbon fibers according to claim12, wherein the densifying step includes: a step of making a solventpermeate through the aggregate of the carbon fibers; and a step ofdrying the aggregate of the carbon fibers and the solvent.
 14. Themethod of manufacturing an aggregate structure of carbon fibersaccording to claim 12, wherein the densifying step includes: a step ofmaking a solvent containing an adhesive substance different from thecarbon fibers permeate through the aggregate of the carbon fibers; and astep of evaporating the solvent.
 15. The method of manufacturing anaggregate structure of carbon fibers according to claim 13, wherein thesolvent is selected from a group of N,N-dimethylformamide,dichloroethane, isopropyl alcohol, ethanol and methanol.
 16. The methodof manufacturing an aggregate structure of carbon fibers according toclaim 13, wherein the solvent contains interfacial active agents orfunctional macromolecules. 17.-20. (canceled)